Method of operating a blast furnace



NOV- 17, 1964 o. A. THOMAS ETAL METHOD 0F OPERATING A BLAST FURNCE Filed Jan. 23, 1962 United States Patent O @PERATENG A BLAST FURNACE @gelen A. Thomas, Huntington, 'vl Va., and Lee L lvleinert and Harold G. Boulton, Ashland, Ky., assignors to Ashland @il @c Refining Company, Ashland, Ky.,

a corporation of Kentuclry Filed Jan. 23, 1%2, Ser. No. 163,26) lll laims. (Cl. l5-42) This invention relates to the operation of a blast furnace for reducing iron ore to metallic iron. More particularly, the invention relates to a method of operating a blast furnace using a fuel which comprises a slurry of particulate coal suspended in-oil.

In the conventional method of operating a blast furnace, the furnace is charged with a mixture principally of iron ore, coke and limestone, usually with lesser amounts of other iiuxing and/or metallurgical materials. The colte supplies fuel for heating the mass and also comprises a reducing agent for reducing the iron oxide of the ore to the basic metal. Air preheated to a temperature of about 100G-2500" F. is blown into the furnace under pressure through ports or tuyeres near the bottom of the furnace. Under the conditions in the furnace, the coke burns incompletely in the air to form carbon monoxide, which reduces the ore to ironwith the accompanying formation of carbon dioxide. The limestone is a slag-forming ingredient, and combines With various siliceous impurities or gangue in the ore to form a slag which floats on the molten iron at the bottom of the furnace. Carbon monoxide, carbon dioxide and the inactiveV atmospheric gases travel upwardly through the charge or burden, and are collected at the top of the furnace and used to supply heat to stoves in which the incoming air is preheated.

Inside the furnace, the temperature in the region adjacent the tuyeres, called the raceway, is very high, typically about 3600 F., at which temperature the iron is a white hot liquid. The ore and coke and the vlimestone burden are supported over the pool of iron, and the colte is continually burned away at the bottom, which causes a gradual settling of the burden and colte in the furnace. The burden is rendered relatively permeable to the blast by the coke and in some cases by the use of pelletized or treated ore, so that the blast can penetrate upwardly through it and so that the burden will settle more evenly as the coke burns away at the bottom. Such operation is conventional and affords the background for this invention.

In accordance with the present invention, at least a part of the conventional coke charge is replaced by a mixture or slurry of relatively coarse coal particles suspended in oil, which is injected into the furnaceeither directlyor through the tuyeres. We have found that a coal-oil slurry of the type to be described possesses excellent characteristics as a metallurgical fuel. Moreover, both oil and coal are relatively less expensive than coke, and their use in place of colte substantially reduces overall fuel costs of blast furnace operations in many instances. Slurry fuels also afford more flexible control over furnace operation, in that the fuel input can readily be adjusted to meet changing conditions, Whereas the rate at which the conventional coke charge burns is subject to relativelylittle control.

In conventional blast furnace operation, the temperature of the air blast which is blown into the furnace is limited by the fact that too high a blast temperature will cause partial melting of the unreduced burden high above the tuyeres, and will cause the burden to bridge over and hang up on the furnace walls, with subsequent abrupt and dangerous slippage This is caused by a lack of sufficient carbon monoxide to reduce the iron oxide in the region where the bridging tends to occur. ln many cases,

3,15 l ,49 l Patented Non. 17, 1954 ICC even though the furnace top gas may have sufficient heat content to preheat the blast many degrees higher, such excess hea cannot be used because the resultant higher enable the furnace to utilize excess heat available for the blast, yet `provide sucient quantities of reducing gases to reduce the ore higher in the furnace and thereby mim'- mize hang-ups.

Fuel oil itself has heretofore been used as a blast furnace fuel. We have found, however, that a fuel oil-coal slurry, when produced and used in accordance with the method to be described, affords important economic advantages over fuel oil alone. In many cases, coal isless expensive than either coke or oil, and, if properly used with oil, will still further improve the favorable economics of oil alone. t

ln the process we have invented, coal is comminuted or ground to particles the nominal maximum size of which is about 1/16 to 3%. This coal is mixed with fuel oil in the approximate proportions of 40-70% by weight coal to 60 to 30% oil. The oil used may be a heavy fuel oil or a residual oil, preferably a so-called No. 6 oil or Bunker C oil, having a Saybolt Furol viscosity of between and 1000 seconds at 122 F., and is heated to a temperature of about 15G-300 F. or higher. Y

Upon mixing, the coal forms a dynamic suspension with the oil. On account of the relatively coarse size of the coal particles, the major portion of which usually will not pass a No. 40 screen, the suspension is highly unstable, and the particles tend to settle out rapidly. We have found, however, that even at these very high solid contents such a slurry can be pumped and handled as a liquid if itis kept in constant movement. Preferably this is effectedl by preparing the slurry on a continuous basis at the rate at which it is to be used, and by agitating the slurry up to the time it is pumped to the blast furnace. Surprisingly, even very low velocities of movement are sufficient to keep the coal particles in suspension, even where the maximum particle size is 1A or larger; for example, a slurry in accordance with this invention will remain in dynamic suspension when moving in a 11/2" pipe at a flow rate of 0.1 foot per second. In general, the apparent viscosity of the slurry mixnire depends primarily on the size gradation of the coal. The minimum ow velocity for maintaining the coal particles in suspension also depends primarily on the gradation of the coal.

In the past, mixtures of coal in oil have been used as fuels, but such mixtures have been in the form of stable dispersions of very finely ground coal, e.g. fine enough that of the coal particles will pass a 200 mesh screen, and such fuels have been dependent on the incorporation of various additives and/ or processing operations to make them stable. Peptizing agents have been incorporated in coal-oil mixtures to stabilize the mixtures and hold the coal particles from settling. Prior art dispersion fuels have thus been relatively expensive to produce by reason of the very fine size to which the particles necessarily were vreduced and also on account of the additives and extra processing techniques which were used. The present process does not depend on the formation of a stable dispersion, nor on the reduction of coal to very fine particle sizes, yet provides excellent results in blast furnace operation at relatively low cost through the use of an inherently unstable suspension.

The proportion of coal in the slurry should be as Ylarge as possible, and in practice it has'been found that dispersions of 55-65 or higher are desirable for most economical operation of the furnace. Prior art coal-oil fuels were vusually/'limited to maximum coal contents of 30 or '40%,

Yspecic oil used, the distribution of particle sizes in the coal, the proportion of coal in the slurry, and the tem-V peratureY of the mixture. In general, the viscosity of theV mixture decreases rapidly with increasing temperatures; for example, in one instance eating the slurry from 150 F. to 180 F. decreased its viscosity from 4250 seconds, Saybolt Furol, to 2040. Y In the present process, the slurry is heated to a temperature of at least150 F. and'preferably as highas 300 F. or higher if possible in view of flash pointrconsiderations, so that itrwillrbe more easily pump-J able'even at the very high solids content which is present.

Once the coal has been mixed with the oil,'the slurry is constantly agitated until used. Preferably the fuel is mixed continuously at the rate at which it is used, so that it does not needrto be stored, although it may be prepared on a batch basis, The fuel ispumped to the blast furnace,V

being kept in motion as this is done. Y

As previously suggested, the pumpability of theV slurry j depends substantially on the proportion Vof fines Which it contains; nas great a proportion as possible of coal in the slurry is desirable, :but too many fines tend to dry it up and render the mixture too heavyto pump. ln practice, so-called natural grind coal having a nominal maximum particle size of about 1/iVor can be mixed with fuel oil in amounts up to 60 or 70% and yet remain pumpable. Suchra mixture contains a far greater proportion of solids Vthan prior art fuels of the stable dispersion type.

The slurry is injected directly into the hot air or blaststream which is blown into the furnace throughV the tuyeres, or is injected directly into the furnacethrough the wall proper.` If theoii comes into Vdirect contact with the'tuye're Wall, it tends to carbonize vsornevvhat at the prevalent high temperature, and for that reason it is preferred to inject the slurry into the tuyere opening lthroughV a lance, the slurry being injected into the blast stream substantially along thek axis of the tuyere so that it does not coat the tuyere Walls. 1 Alternatively, `the slurry can be introduced into the blast froman'opening in vlthe/top wall of the tuyere, where it Will be picked up by the blast and carried immediately into Vtheinterior of the furnace. In general, it canbersaidrthat if the point at which the Vslurry is injected into the furnace is too close to the race- Way, the fuel Will not burn sutciently for optimum operation, and if it is injected too far from the raceway, it

may ignite too early andoverheat the injection port.

Inside the furnace, the coal and oil are ignited by the high temperature ,ofthe blast. Combustion .of the coal f releases carbonrmonoxid'e and some hydrogen from the proportion added will depend on the quality of iron to be produced; the relative cost of oil, coal, and coke, the use made of the top gas, furnace efciency, the value of the slag which is produced, and other factors. should benoted, however, thatthe use of a coal and oil slurry in accordance with this process is not neeessarily intended to eliminate all of Athecoke used in the Typically, the slurry will replace some but A major reason for the continued burden. not all of the coke.

use of coke in the burden is that it imparts permeability to theV burden so that the hot blast'can travel upwardlyV vthrough the furnace.

It is noted that prepared, eg. sintered, ores themselves impart permeability `to the burden, and their use in the charge will make it possible. Y

to replace a greater portion ofthe coke inthe burden with the coal-oil slurry of this invention.

The drawing is a diagrammatic illustration ofthe.V

practice of the present processen a continuous basis.

Following is a detailed example of they present process. Y

v Example A medium viscosity No. 6 fuclrhaving the Yfollowing characteristics was usedras the liquid constituent of the slurry: i

API gravity 17.2 Specific gravity at 60 F. 0.953 Viscosity at 122 F., SE. V164. FlashfCOC 285 BS & W Trace Using conventional equipment, coal was comminuted to a nominal 1A x O'size.VV The sizev gradation of this coal was: Y

Screen No.-

6 .L S '95 16 74 30 5,1 50 28 100 y 7 200 4 I The coal incorporated in the slurry may be scalped olf volatiles in the coal which, with the carbon rnonor'rideV produced by the colte in the charge, reduces the ore. Y'

Partial combustion kof, the yhydrocarbon fuel produces carbon monoxide and, more importantly, hydrogen, which is several times more effective thanfcarbon monoxide `as a reducing agent. vThe hydrogen which is produced from the burning oil and coal combines with the oxygen of the ore to 'formu/ater,v and thereby producesrhot metal. Byl 65 reason of the highly reducing atmosphere providedrby thegburning hydrocarbons, an excess of hydrogen. is avail- `Y able forreducing the ore higher'lin the furnace, '1 minimizing hangupsfand permitting higher blast temperatures to be'used. Moreover, some unreacted hydrogen will be presentrin the top gas fromr thefurnace, which Will. en- 'f Vrich its heatingfvalue and improve the economics ofV the preheating operation. Y

The rate at whichjthe'fgiurry is added to the blast depends upon several variables, and cannot be concisely Y specified for any and all conditions. In general, the

yof the Water in situ. A wide variety of coalscan bel used pending onV the typekof blast furnace operation underV larger grind coal; thus, forcxarnple, 1/2". x 0 sizecoal maybe scalped to 1% x VOto 1/pig Vx 0 size coalfor Y slurry V.

An important economic advantage of the present process'is that the coal does not need to be specially dried before it is mixedrwith the oil. Usually commercial granular coal has a waterV content vof roughlyV 6 to 9%,

and Where powdered coal itself is used as a fuel, i.e.,

not mixed with oil7 itmust be dried to a very low moisture content to Ybe owable. in the present process, such moisture content is not harmful, vandthe coalneed not Y befurther dried. In factpthe hot oil evaporate's much in the slurry, de

consideration. For example, since the oil supplies hy? drogen, low volatility coals can ybe used.

VThe oil Washeated to a'temperature'of about 190 F.,

andrwas pumped into' a slurry mix tank; The coal was added Vto the oil in such amount as to comprise V60% Vby vveight of .the resultant slurry. The slurry was continuouslyr'agitatcd in the mix tank by a turbinefmixerlor theequivalenaand'even the largest particles remainedl in effective suspension. The ,mixtureV was maintainedtat a temperature of aboutl- F., and v.displayed Va'vis'cosity of 14,690 secondsS.S.U.fand a'specicgravity of 1.156'.V lf desired, additives may bereadilyvadded to the slurry in mixing tank, e.g. viscosity lowering agents, stabilizers and the like, but Vthese willnot ordinarily be necessary.

jThe use of aslurry system has a furtherrinherent ad- V :Avantage'in comparisonl to Vconventional blast furnace nv f Total percent passing E? operating techniques in that limestone, coke breeze, flue dust, and other difficult to inject materials or additives can be added to the slurry to give additional operating benefits with regard to economics, blast furnace operations, and control.

The slurry was delivered to the blast furnace through a 11/2 pipe, and is preferably pumped by a Moyno Pump of the rotatingy screw type, made by the Mayno Pump Division of Robbins & Myers Company, Inc., of Springlield, Ohio.

The size of the uid conduit through which the slurry is delivered to the furnace appears to be fairly critical for any given slurry. If the pipe is too small in diameter, or is too long, an excessively high pressure will be required to force the slurry through it at a rate suicient to keep the coal particles from settling out; and if the pipe is too large in diameter, the velocity of fluid movement may be so low for a given pressure drop that the particles will settle out. In practice, for any given slurry there is a limited range of conduit sizes through which the slurry can be pumped With available pumping equipment and without the coal particles settling out.

The slurry can be introduced into each tuyere of the furnace through a 3%" or 1 lance. in general, the size of the lance will depend on the top size of the particles in the slurry. For example, if the top particle size is about 1/8, then a 3/M lance can be used, whereas if top particle size is 1A it is preferable to use 1 lance. It should be stated that the use of a lance in the tuyere does present the disadvantage of partly blocking the tuyere opening, which disadvantage is not encountered if the slurry is injected directly into the tuyere through an opening in its wall, or an opening in the blowpipe.

The velocity of the air blast at the tuyere is very high, typically about 3D0-600 feet per second, and the blast carries the pariculate slurry into the raceway of the furnace even though some of the particles are relatively heavy. Tests have shown that the coal particles do not settle out appreciably in the iiuid conduits, provided conduits of suitable size are used and provided the uid is constantly kept in motion.

Injected into the furnace, the slurry provides more efficient and economic furnace operation, as previously explained. The capacity of the furnace is increased, and hot metal is produced at lower cost.

The present invention has been described herein primarily in relation to the operation of a blast furnace, in which its primary utility is at present believed to reside. However, the slurry produced in accordance with this process is quite suitable for use as a fuel in other types of furnaces, and it will be understood that it is not limited to use in a blast furnace alone.

What is claimed is:

1. The method which comprises, sizing coal to a maximum particle size of about j/1(; to 3/s, mixing said coal with a fuel oil having a viscosity in the range of about 75-1000 seconds S.F. at 122 F. to form an unstable slurry which consists essentially of Said coal and said oil and in which said coal is suspended in said oil, said coal comprising about ttl-70% by weight of said slurry and said oil comprising about 6030% of said slurry, heating said oil and maintaining it at a temperature of about ISO-300 F. as said coal is being mixed therewith, whereby the viscosity of said slurry is reduced, maintaining said coal in suspension in said slurry by agitating said slurry and keeping said slurry in movement, and introducing said slurry into a furnace.

2. The method of claim 1 wherein said slurry is delivered to said furnace at a flow velocity at which said coal is maintained continuously in suspension in said slurry.

3. The method of claim 1 wherein said slurry is kept in movement at a velocity not less than about 0.1 foot per second.

4. The method which comprises, comminuting coal to a maximum particle size of about 1/16 to SAV', mixing said coal with a fuel oil having a viscosity in the range of about -1000 seconds SF. at 122 F. to form an unstable slurry in which said coal is suspended in said oil, said coal comprising about 40-70% by weight of said slurry and said oil comprising about 6030% of said slurry, heating said slurry to a temperature of about 15G- 300 F. whereby the viscosity of said slurry is reduced, maintaining said coal in suspension in said slurry by agitating said slurry and keeping said slurry in movement, and introducing said slurry into the air blast of a blast furnace, said slurry being heated to said temperature prior to its introduction into said air blast.

5. The method of claim 4 wherein said slurry is injected into said furnace through a tuyere thereof.

6. The method of claim 4 wherein said slurry is injected into said furnace through a tuyere thereof, said tuyere having a lance Iformed in it, said slurry being injected into said furnace through said lance.

7. The method which comprises, preparing natural grind coal to a nominal size in the range of 1/16" x 0 to 1A x 0, mixing said coal with a fuel oil having a viscosity in the range of about 75-30() seconds SF. at 122 F. to form an unstable slurry in which said coal is suspended in said oil, said coal comprising about 50-70% by weight of said slurry and said oil comprising about 5-30% of said slurry, simultaneously heating said slurry to a temperature of about 1GO-250 F., maintaining said coal in suspension in said slurry by agitating said slurry and keeping said slurry constantly in movement, and injecting said slurry into the hot air blast of a blast furnace.

8. The method which comprises, sizing coal to a nominal size of about 1A X 0, the major portion of said coal being able to pass a No. 36 screen, mixing said coal with a fuel oil having a viscosity in the range of about -275 seconds SE. at 122 F. to form an unstable slurry in which said coal is suspended in said oil, said coal comprising about 55-65% by weight of said slurry and said oil comprising about l5-35% of said slurry, heating said slurry to a temperature of about,160-195 F. whereby the viscosity of said slurry is reduced, maintaining said coal in suspension in said slurry by agitating said slurry and keeping said slurry constantly in movement, and then pumping said slurry into the air blast of a blast furnace.

9. A method of producing a pumpable slurry of coal in oil having a high solids content, said method comprising, sizing coal to a nominal maximum particle size of about AS" to mixing said coal with fuel oil to form a unstable slurry in which said coal is suspended in said oil, said coal comprising about 40-70% by weight of said slurry and said oil comprising about 60-30% of said slurry, heating and maintaining said oil at a temperature of about 15G-300 F. during and subsequent to the mixing of said coal with said oil and prior to and substantially during the pumping thereof, and maintaining said coal in suspension in said slurry by agitating said slurry and keeping said slurry in constant movement, whereby said slurry is rendered pumpable.

10. The method of claim 9 wherein said slurry is kept in constant movement at a rate not less than about 0.1 foot per second.

References Cited bythe Examiner UNITED STATES PATENTS 1,507,740 9/24 Kirby 75-42 2,938,782 5/60 Toulmin 75-42 DAVID L. RECK, Primary Examiner. W INSTON A. DOUGLAS, Examiner.

UNITED STATES PATENT oEEICE QERTIFICATE 0F CGRRECTION Patent No. 3,157,491 November 17, 1964 Ogden A. Thomas et a1.

certified that error appears in the above numbered pat- It is hereby and that the said Letters Patent should read as ent requiring correction corrected below.

Column 4, 1ne 1, for "quality" read quantity column 5, line 8, for Mayno" read Moyne".

Signed and sealed this 10th day of May 1966.

(SEAL) Attest:

EDWARD J. BREWER Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. THE METHOD WHICH COMPRISES, SIZING COAL TO MAXIMUM PARTICLE SIZE OF ABOUT 1/16" TO 3/8", MIXING SAID COAL WITH A FUEL OIL HAVING A VISCOSITY IN THE RANGE OF ABOUT 75-1000 SECONDS S.F. AT 122*F. TO FORM AN UNSTABLE SLURRY WHICH CONSISTS ESSENTIALLY OF SAID COAL AND SAID OIL AND IN WHICH SAID COAL IS SUSPENDED IN SAID OIL, SAID COAL COMPRISING ABOUT 40-70% BY WEIGHT OF SAID SLURRY AND SAID OIL COMPRISING ABOUT 60-30% OF SAID SLURRY, HEATING SAID OIL AND MAINTAINING IT AT A TEMPERATURE OF ABOUT 150-300*F. AS SAID COAL IS BEING MIXED THEREWITH, WHEREBY THE VISCOSITY OF SAID SLURRY IS REDUCED, MAINTAIN- 